Abstract &#947;&#948;T cells play roles in immune regulation and tumor resistance, although how they carry out these functions remains poorly understood. The overall objective of this project is to further understand &#947;&#948;T cell function by identifying and characterizing ligands for &#947;&#948;T cell receptors (TCRs). Using soluble &#947;&#948;TCR multimers (smTCRs), and in particular a newly developed self-pentamerizing mouse smTCR, we can detect putative ligands. Based on preliminary work, we hypothesize that &#947;&#948;TCR ligands are most commonly cellsurface host-encoded protein molecules, whose expression is induced during inflammation. Our aims are: Specific Aim 1 - To identify the ligands for two common mouse &#947;&#948;TCRs, the invariant V&#947;6V&#948;1+ TCR and a typical V&#947;1V&#948;6.3+ TCR. We hypothesize that the ligands for these two TCRs are cell surface protein molecules encoded by a single gene, expressed by certain cells and induced during inflammation. These ligands will be identified using expression cloning, based on soluble multimeric &#947;&#948;TCRs (smTCRs) as reagents to detect their own ligands, or via a proteomics approach. Candidates will be verified by functional tests. Specific Aim 2 - To generate smTCRs representing two recently discovered subsets of &#947;&#948;T cells with defined functions, and to identify their ligands. We have recently discovered two new functionally distinct subsets of &#947;&#948;T cells - one expressing a V&#947;4V&#948;4 TCR with highly restricted junctional regions that responds during collagen-induced arthritis, and the other a V&#947;1V&#948;5 TCR that promotes airway hyperreactivity. Our hypothesis is that these two &#947;&#948;TCR types recognize a particular host protein ligand whose expression is induced or enhanced in the course of the relevant disease. Two new self-pentamerizing smTCRs representing the TCRs expressed by these two subsets will be generated to further investigate the ligand each recognizes. Specific Aim 3 - To investigate the possibility that mice and humans express certain conserved &#947;&#948; TCR ligands, which are recognized by conserved V&#948;chains. We hypothesize that several closely related mouse and human V&#948;genes may also be functionally equivalent. We plan to test whether mouse &#947;&#948;smTCRs can detect potential ligands on relevant human cells or cell lines, and will generate mouse/human recombinant &#947;&#948;TCRs to test whether a mouse V&#948;can be replaced by its human V&#948;equivalent. Taken together, these studies will provide insight into the mechanism of &#947;&#948;TCR-ligand interactions and their conservation between mice and humans. This information will be useful in future studies of &#947;&#948;T cell immunobiology, and could ultimately provide a basis for treatment strategies in diseases such as autoimmunities, infectious diseases, and cancer.